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Terms

an electric current in which the direction of flow of the electrons reverses periodically having an average of zero, with positive and negative values (with a frequency of 50 Hz in Europe, 60 Hz in the US, 400 Hz for airport lighting, and some others); especially such a current produced by a rotating generator or alternator.

Nikola Tesla (Serbian Cyrillic: Н Т; 10 July 1856 – 7 January 1943) was a Serbian-American inventor, physicist, mechanical engineer, electrical engineer, and futurist. He was an important contributor to the use of commercial electricity, and is best known for his contributions to the modern alternating current (AC) electrical supply system.

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The Telephone

Alexander Graham Bell is commonly credited as the inventor of the first practical telephone. He was the first to obtain a patent, in 1876, for an "apparatus for transmitting vocal or other sounds telegraphically", after experimenting with many primitive sound transmitters and receivers.

Bell's telephone transmitter (microphone) consisted of a double electromagnet, in front of which a membrane, stretched on a ring, carried an oblong piece of soft iron cemented to its middle. A funnel-shaped mouthpiece directed the voice sounds upon the membrane, and as it vibrated, the soft iron "armature" induced corresponding currents in the coils of the electromagnet. After traversing the wire, these currents passed through the receiver, which consisted of an electromagnet in a tubular metal can that had one end partially closed by a thin circular disc of soft iron. When the undulatory current passed through the coil of this electromagnet, the disc vibrated, thereby creating sound waves in the air [[fig:7359].

The first long distance telephone call was made on 10 August 1876 by Bell from the family homestead in Brantford, Ontario, to his assistant located in Paris, Ontario, some 10 miles away. In June 1876, Bell exhibited a telephone prototype at the Centennial Exhibition in Philadelphia.

The Lightbulb

Thomas Alva Edison's major innovation was the first industrial research lab, which was built in Menlo Park, New Jersey and was the first institution set up for the specific purpose of producing constant technological innovation. Most of the inventions produced there were legally attributed to Edison, though many employees carried out research and development under his direction.

Edison did not invent the first electric light bulb, but rather the first commercially practical incandescent light. Many earlier inventors had previously devised incandescent lamps, including Henry Woodward and Mathew Evans. Others who developed early and commercially impractical incandescent electric lamps included Humphry Davy, James Bowman Lindsay, Moses G. Farmer, William E. Sawyer, Joseph Swan, and Heinrich Göbel. These early bulbs had an extremely short life, were expensive to produce, or drew a high electric current, making them difficult to produce on a large commercial scale.

By 1879, Edison had produced a new concept: a high resistance lamp in a very high vacuum, which would burn for hundreds of hours. While earlier inventors had produced electric lighting in laboratory conditions, dating back to a demonstration of a glowing wire by Alessandro Volta in 1800, Edison concentrated on commercial application. He was able to sell the concept to homes and businesses by mass-producing relatively long-lasting light bulbs and creating a complete system for the generation and distribution of electricity.

The "War of Currents"

Edison's true success, like that of his friend Henry Ford, was in his ability to maximize profits by establishing mass-production systems and obtaining intellectual property rights. George Westinghouse became an adversary of Edison when he promoted the direct current (DC) for electric power distribution instead of the more easily transmitted alternating current (AC) system invented by Nikola Tesla and promoted by Westinghouse. Unlike DC, AC could be stepped up to very high voltages with transformers, sent over thinner and cheaper wires, and stepped down again at the destination for distribution to users.

The problem with DC was that power plants could only economically deliver DC electricity to customers within about one and a half miles (about 2.4 km) from the generating station, so that it was only suitable for central business districts. When George Westinghouse suggested using high-voltage AC instead, as it could carry electricity hundreds of miles with only marginal loss of power, Edison waged a "War of Currents" to prevent the adoption of the AC system.

The war against AC involved Edison in the development and promotion of the electric chair (using AC) as an attempt to portray AC to have greater lethal potential than DC. Edison continued to carry out a brief but intense campaign to ban the use of AC or to limit the allowable voltage for safety purposes. As part of this campaign, Edison's employees publicly electrocuted animals to demonstrate the dangers of AC. On one of the more notable occasions, Edison's workers electrocuted Topsy the elephant at Luna Park, near Coney Island, after she had killed several men and her owners wanted her put to death.

AC eventually replaced DC in most instances of generation and power distribution, enormously extending the range and improving the efficiency of power distribution. Though widespread use of DC ultimately lost favor for distribution, it exists today primarily in long-distance high-voltage direct current (HVDC) transmission systems.

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